Intermolecular Forces & Gases: Lewis Structures & VSEPR Theory

Terminology and molecular geometries associated with Lewis structures and VSEPR theory as described in the lecture notes.

Lewis Dot Structure

A representation showing the arrangement of valence electrons in a polyatomic ion or molecule.

VSEPR Theory

Valence Shell Electron Pair Repulsion theory, which states that molecules take their shape based on the repulsion between bonding and non-bonding electron groups in the valence shell of the central atom.

Central Atom

The least electronegative element in a molecule (excluding hydrogen) that connects to the outer atoms.

Octet Rule

The principle that a central atom will usually have 8 valence electrons.

Electron Group

In VSEPR theory, a single unit of electron density which can consist of a single covalent bond, a double covalent bond, a triple covalent bond, or a lone pair of electrons.

Bond Angle

The angular separation between the central atom and two bonded atoms, such as $109.5^\text{o}$ for Methane ($CH_4$).

Linear Geometry

A molecular shape with 1 or 2 electron groups around the central atom and a bond angle of $180^\text{o}$, as seen in $CO_2$.

Trigonal Planar

A molecular shape characterized by 3 electron dense areas with 0 lone pairs and a bond angle of $120^\text{o}$.

Bent (3 electron dense areas)

A molecular geometry with 3 electron groups including 1 lone pair, resulting in a bond angle of $117.5^\text{o}$.

Tetrahedral

A molecular shape formed by 4 electron dense areas with 0 lone pairs and a bond angle of $109.5^\text{o}$.

Trigonal Pyramidal

A molecular shape formed by 4 electron dense areas with 1 lone pair and a bond angle of $107^\text{o}$.

Bent or V-shape (4 electron dense areas)

A molecular geometry formed by 4 electron groups including 2 lone pairs, resulting in a bond angle of $104.5^\text{o}$.